Abstract
Bulk bismuth presents outstanding optical properties, such as a giant infrared refractive index (n∼10) and a negative ultraviolet-visible permittivity induced by giant interband electronic transitions. Although such properties are very appealing for applications in nanophotonics, the dielectric function of bismuth nanostructures has been scarcely studied. Here, we determine by spectroscopic ellipsometry the far infrared-to-ultraviolet dielectric function of pulsed laser deposited bismuth thin films with nominal thickness tBi varied from near 10 nm to several tens of nm. For tBi > 15 nm, the films display a continuous structure and their dielectric function is comparable with that of bulk bismuth. For tBi < 15 nm, the film structure is discontinuous, and the dielectric function differs markedly from that of bulk bismuth. It is proposed from FDTD simulations that this marked difference arises mainly from effective medium effects induced by the discontinuous film structure, where quantum electronic confinement does not play a dominant role. This suggests that ultrathin and continuous bismuth films should present the same outstanding optical properties as bulk bismuth for high performance nanophotonic devices.
Highlights
Bulk bismuth (Bi) presents outstanding optical properties, related with its giant interband electronic transitions, such as a giant infrared refractive index (n ∼ 10) and a negative ultraviolet – visible permittivity [1]
It is proposed from finite difference time domain (FDTD) simulations that this marked difference arises mainly from effective medium effects induced by the discontinuous film structure, where quantum electronic confinement does not play a dominant role
From an analysis based on FDTD simulations, we propose that such different dielectric function is the result of the effective medium behavior of the discontinuous film
Summary
Bulk bismuth (Bi) presents outstanding optical properties, related with its giant interband electronic transitions, such as a giant infrared refractive index (n ∼ 10) and a negative ultraviolet – visible permittivity [1] These properties are thought to enable a strong visible and infrared absorption [1,2,3,4] and an ultraviolet – visible plasmonic response [1,2,3,5,6] in deeply subwavelength Bi nanostructures. For exploiting the full potential of such applications by rational nanostructure design, knowing the dielectric function of Bi nanostructures in a broad spectral range, from the far infrared to the ultraviolet, is needed Such data are not available, despite of several claims of quantum electronic confinement effects implying a size-dependence for the electronic structure of bismuth nanostructures [15,16,17,18]. This leads us to propose that the observed deviation does not primarily originate from quantum electronic confinement
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